Ch 23 Cancer Genetics

Question 1

what is cancer?

Answer 1

a heterogenous group of disorders characterized by the presence of cells that do not respond to normal cell division

Question 2

what is a tumor?

Answer 2

a distinct mass of abnormal cells

Question 3

what is meant when cancer is benign?

Answer 3

tumor cells remain localized

Question 4

what is meant when cancer is malignant?

Answer 4

tumor cells invade other tissues

Question 5

what is meant when cancer is metastatic?

Answer 5

tumor cells travel to other sites where they can establish secondary tumors

Question 6

how can cancer be nongenetic?

Answer 6

• if cancer is inherited, every cell should have cancer, caused by the cancer causing gene
• tumors appear only in some tissues
• tumors often appear when a certain age is reached

Question 7

what does Knudsen’s proposal suggest about cancer?

Answer 7

cancer is a multistep process that requires several mutations

Question 8

explain the clonal evolution of tumors

Answer 8

mutations enhance cells’ ability to proliferate and become the most common cells in a clone, allowing the clone to become increasingly rapid in growth and aggressive in proliferation properties

Question 9

normal cellular gene responsible for normal cell gunction

Answer 9

proto-oncogene

Question 10

gene that stimulates cell division, leading to tumors forming and cancer

Answer 10

oncogene

Question 11

are oncogenes dominant or recessive acting? why?

Answer 11

dominant-acting; the amount of gene product produced by one allele is enough to have a stimulatory effect

Question 12

genes that normally inhibit cell division

Answer 12

tumor-suppressor genes

Question 13

are tumor-suppressor genes dominant or recessive acting? why?

Answer 13

both copies of the allele must be mutated to remove inhibition

Question 14

inactivation of remaining wild-type allele of a heterozygote

Answer 14

loss of heterozygosity

Question 15

appearance of mutant phenotype in individual that is heterozygous for the trait

Answer 15

haploinsuffiency

Question 16

explain how mutations in (proto)oncogenes can contribute to cancer?

Answer 16

a mutation in a proto-oncogene results in an oncogene that stimulates cell division without normal controls, leading to cell proliferation

Question 17

explain how mutations in tumor-suppressor genes can contribute to cancer?

Answer 17

a mutation in a tumor-suppressor gene prevents the gene from inhibiting cell division, leading to excessive cell proliferation

Question 18

what are the roles of CDKs? how are they functional?

Answer 18

CDKs add phosphate groups to other proteins, either activating or inactivating the protein
they are functional only when they are associated with cyclin

Question 19

what are the roles of cyclin and how do they contribute to the cell cycle?

Answer 19

cyclins associate with CDKs, activating them and making them function. cyclins levels oscillate during the cell cycle, allowing the cell to pass through certain stages

Question 20

describe the G1-S transition
(what checkpoint? what proteins are involved? how does the cell transition into the next stage?)

Answer 20

retinoblastoma (RB) protein binds to E2F, inactivating it
as cyclins D & E increase in G1, they associate with CDKs and phosphorylate RB, inactivating it, which releases E2F
E2F goes to transcribe products necessary for DNA replication –> S phase

Question 21

what is the role of the retinoblastoma (RB) protein in the G1-S transition?

Answer 21

RB prevents the cell from passing the G1/S checkpoint by binding E2F and inactivating it

Question 22

what would happen if there was a mutation in the RB protein?

Answer 22

the RB protein won’t be able to bind and inactivate E2F, therefore cell division is always occurring without normal controls

Question 23

describe the G2-M transition

Answer 23

inactive MPF (cyclin-B + CDK) is dephosphorylated, and critical levels of active MPF allow cell to enter mitosis and divide

Question 24

what is the mitosis-promoting factor (MPF) composed of?

Answer 24

cyclin-B and CDK

Question 25

what occurs when cyclin-B levels increase in G2

Answer 25

increasing cyclin-B concentrations combine with CDKs to form active MPFs, which phosphorylates other proteins that bring about events of mitosis

Question 26

what happens in metaphase, regard cyclin levels?

Answer 26

cyclin-B is rapidly degraded in metaphase, which lowers the amount of active MPF, bringing about events that end mitosis

Question 27

what is p53 and what is it regulate?

Answer 27

p53 is a tumor-suppressor gene; regulate an inhibitor of CDK

Question 28

what would happen if there was a mutation in the p53 gene?

Answer 28

CDK activity would stay constant, causing cell proliferation

Question 29

programmed cell death

Answer 29

apoptosis

Question 30

how does apoptosis relate to cancer?

Answer 30

cancer cells usually have defects in cellular components that stimulate apoptosis, and cells that need to die proliferate

Question 31

how does autophagy relate to cancer?

Answer 31

autophagy allows cancer cells to s

Question 32

explain how the Ras signal transduction pathway is important in the cell cycle

Answer 32

external growth factors bind to receptors that allow adapter molecules to bind, which link to an inactive Ras protein. Ras binds GTP, activating, and activates a series of steps, resulting in the activation of transcription factors that transcribe genes of the cell cycle

Question 33

how do mutations in Ras genes contribute to cancer?

Answer 33

mutations in Ras genes produce mutant Ras proteins that are always active and continuously stimulate cell division

Question 34

how are DNA-repair genes and mechanisms associated with cancer?

Answer 34

defects in DNA-repair genes prevent DNA-repair mechanisms fixing defects in genes that may contribute to cancer

Question 35

explain how mutations in telomerase expression contribute to cancer?

Answer 35

mutations in telomerase lead to telomerase being constantly expressed in somatic cells, which allows for unlimited cell division

Question 36

growth of new blood vessels

Answer 36

angiogenesis

Question 37

how do mutations in genes that promote vascularization contribute to cancer?

Answer 37

tumors need oxygen and nutrients to survive. mutations in genes that promote the growth of new blood vessels allows these tumors to stay and grow

Question 38

why would a reduction in miRNAs contribute to cancer?

Answer 38

miRNAs are responsible for degrading or inhibiting the translation of mRNA
reduction in miRNAs may allow oncogenes that are normally suppressed to be highly expressed

Question 39

explain how hypomethylation is associated with cancer

Answer 39

lowered DNA methylation leads to transcription of oncogenes that allow for cancer

Question 40

explain how hypermethylation is associated with cancer

Answer 40

higher DNA methylation leads to tumor-suppressant genes being inhibited